The long term objective of this work is to determine the sequential cellular changes following irradiation leading to mammary tumor formation. Experiments using the cell dissociation (CD) and epithelial focus (EF) assays over the last project period have provided information on cellular changes based on in vivo and in vitro growth parameters. Cell lines were also developed which have been used to study neoplastic progression. The proposed experiments are designed to take advantage of the unique opportunities made possible with these model systems to extend these studies to examine the role of chromosome alterations, oncogenes and growth factors in mammary tumor development. Cytogenetic and molecular biologic techniques will be used to more fully characterize tumors and the altered cellular phenotypes observed to precede mammary tumor development. These studies will use tumors as well as tissues, primary cells, and cell lines obtained from the CD and EF assays to: (1) determine whether specific chromosomal alterations are associated with mouse mammary tumors; (2) determine whether specific chromosomal alterations are associated with phenotypic changes observed during tumorigenesis; (3) determine whether specific oncogenes are associated with mammary tumors; (4) determine whether specific oncogenes are associated with specific altered growth phenotypes during neoplastic progression; and (5) examine biochemical alterations associated with the altered growth phenotypes.